#!/usr/bin/env bash
# 
# 1.5 使用shell进行数学运算

no1=4
no2=5

let result=no1 + no2
echo $result

let no1++
let no1--

let no1+=6
let no1+=6

result=$[ no1 + no2 ]
echo $result

result=$[ $no1 + 5 ]
echo $result

result=$(( no1 + 5 ))
echo $result

result=`expr 3 + 4`
echo $result

result=$(expr $no1 + 5)
echo $result

